You need to install from old to new for it to function properly... So you'll have to install XP on whichever partition first than reinstall Windows 7 on the second partition.. The boot manager will configure itself and everything should be fine as long as you install them in the right order.. Also, a good app to tinker with the boot manager is EasyBCD (available here: Download EasyBCD 1.7.2 - NeoSmart Technologies ). You can set one OS as the default OS and shorten boot selection times, etc with this app.. It's not something you HAVE to have but it's definitely worth checking out.. Good luck..